Spinal fixation plates

ABSTRACT

Spinal fixation plates for maintaining adjacent vertebrae in and fixed position are provided. In an exemplary embodiment, the plate includes opposed superior and inferior portions that are angled in a direction anterior to an anterior face of a mid-portion of the plate. The plate also includes a curvature formed therein about a longitudinal axis in a sagittal plane thereof. In use, when the plate is attached to adjacent vertebrae, the angle of the superior and inferior portions and the curvature in the plate are effective to position one or more thru-bores formed in the superior and inferior portions at the anterior rims of the adjacent vertebrae. In another embodiment, a spinal fixation plate is provided that is adapted to engage and mate to a fusion cage or other vertebral implant disposed between adjacent vertebra. The present invention also provides spinal fixation kits or assemblies, and methods for implanting the same.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.13/912,969, filed on Jun. 7, 2013, which is a continuation of U.S.patent application Ser. No. 12/883,832 (now U.S. Pat. No. 8,591,588),filed on Sep. 16, 2010 entitled “Spinal Fixation Plates,” which is adivisional of U.S. patent application Ser. No. 10/927,778 (now U.S. Pat.No. 7,819,903), filed on Aug. 27, 2004 and entitled “Spinal FixationPlates,” which is a continuation-in-part of U.S. patent application Ser.No. 10/403,930 (now U.S. Pat. No. 7,112,222), filed on Mar. 31, 2003 andentitled “Anterior Lumbar Interbody Fusion Cage With Locking Plate.”These references are hereby expressly incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to medical devices, and more particularlyto spinal fixation plates for promoting fusion of adjacent vertebralbodies.

BACKGROUND OF THE INVENTION

Advancing age, as well as injury, can lead to changes in the bones,disks, joints, and ligaments of the spine producing pain from nerve rootcompression. Under certain circumstances, alleviation of pain can beprovided by performing a spinal fusion. This is a procedure thatinvolves joining two or more adjacent vertebrae with a bone fixationdevice so that they no longer are able to move relative to each other.For a number of known reasons, bone fixation devices are useful forpromoting proper healing of injured or damaged vertebral bone segmentscaused by trauma, tumor growth, or degenerative disc disease. Theexternal fixation devices immobilize the injured bone segments to ensurethe proper growth of new osseous tissue between the damaged segments.These types of external bone fixation devices often include internalbracing and instrumentation to stabilize the spinal column to facilitatethe efficient healing of the damaged area without deformity orinstability, while minimizing any immobilization and post-operative careof the patient.

One such device is a bone fixation plate that is used to immobilizeadjacent skeletal parts such as bones. Typically, the fixation plate isa rigid metal or polymeric plate positioned to span bones or bonesegments that require immobilization with respect to one another. Theplate is fastened to the respective bones, usually with bone screws, sothat the plate remains in contact with the bones and fixes them in adesired position. Bone plates can be useful in providing the mechanicalsupport necessary to keep vertebral bodies in proper position and bridgea weakened or diseased area such as when a disc, vertebral body orfragment has been removed.

Such plates have been used to immobilize a variety of bones, includingvertebral bodies of the spine. These bone plate systems usually includea rigid bone plate having a plurality of screw openings. The openingsare either holes or slots to allow for freedom of screw movement. Thebone plate is placed against the damaged vertebral bodies and bonescrews are used to secure the bone plate to the spine and optionally toa prosthetic implant positioned between the adjacent vertebrae.

While several types of bone fixation plates exists, there remains a needfor improved spinal fixation plates.

SUMMARY OF THE INVENTION

The present invention generally provides spinal fixation plates, spinalimplants for use with spinal fixation plates, and methods for implantingthe same. In one embodiment of the present invention, a spinal fixationplate is provided for maintaining adjacent vertebrae in a fixed positionwith respect to one another. The fixation plate includes a mid-portionwith opposed superior and inferior portions. The superior and inferiorportions can each include at least one thru-bore formed therein forreceiving a fastening element, and the superior and inferior portionsare preferably positioned at an angle with respect to the mid-portionsuch that, when the plate is positioned in relation to adjacent superiorand inferior vertebrae, the superior and inferior portions of the plateare positioned adjacent to the anterior rim of each vertebra. In anexemplary embodiment, the superior and inferior portions are angled in adirection anterior to the anterior face of the mid-portion, and theangle is preferably less than about 15°.

In one exemplary embodiment, the plate can include a posterior curvatureformed about a longitudinal axis. As a result, the plate can have asubstantially concave posterior face, and the plate can also optionallyhave a substantially convex anterior face. In another embodiment, thesuperior and inferior portions of the plate preferably each includefirst and second thru-bore tabs formed on opposed sides of thelongitudinal axis of the plate. When combined with the curvature in theplate, the first and second opposed tabs can be angled toward oneanother in a posterior direction. In an exemplary embodiment, the anglebetween a posterior face of the first thru-bore tab and a posterior faceof the second thru-bore tab in each of the superior and inferiorportions is in the range of about 150° to 180°, and more preferably theangle is about 160°.

In yet another embodiment of the present invention, a spinal fixationplate is provided having a mid-portion and opposed superior and inferiorportions extending at an angle with respect to the mid-portion in adirection anterior to an anterior face of the mid-portion. The superiorand inferior portions each preferably include first and second thru-boretabs formed on opposed sides of a longitudinal axis of the plate. Thefirst and second thru-bores tabs are preferably angled toward oneanother in a posterior direction. The first and second thru-bores tabsin the superior and inferior portions also preferably each include athru-bore formed therein and adapted to receive a fastening element tomate the plate to adjacent vertebrae. The mid-portion can alsooptionally be curved about a longitudinal axis, preferably in aposterior direction, such that opposed side edges of the mid-portion arepositioned posterior to a posterior face of the mid-portion at thelongitudinal axis of the mid-portion. At least a portion of the platecan have a substantially concave posterior face as a result of the curveformed therein. At least a portion of the plate can also optionally havea substantially convex anterior face as a result of the curve formedtherein.

The present invention also provides a spinal fixation kit that includesat least one fixation plate and an implant that is adapted to bedisposed between adjacent vertebra and that has posterior, anterior,superior, and inferior faces. The fixation plate preferably has amid-portion with opposed superior and inferior portions that define aplate length that is preferably greater than a height of the implantbetween the superior and inferior faces. The superior and inferiorportions also preferably include first and second opposed thru-bore tabsthat extend in a direction anterior to an anterior face of themid-portion of the fixation plate, and/or that extend at an angle towardone another in a posterior direction. The kit can also include at leastone fastening element that is adapted to extend through a thru-bore tabin the superior and inferior portions of the fixation plate to mate theplate to adjacent vertebrae.

The present invention also provides methods for implanting a spinalfixation plate. In one exemplary embodiment, the method can include oneor more of the following steps: distracting adjacent vertebrae, removingat least a portion of the disc disposed between the adjacent vertebrae,positioning a spinal implant between the adjacent vertebrae, andpositioning a spinal fixation plate adjacent to an anterior face of thespinal implant such the opposed superior and inferior portions of thespinal fixation plate are positioned on the anterior rim of eachvertebra. A fastening element can then be inserted through one or moreof the thru-bore formed in the spinal fixation plate to attach thespinal fixation plate to the adjacent vertebrae. In an exemplaryembodiment, the superior and inferior portions of the spinal fixationplate include longitudinally opposed thru-bores tabs, each having athru-bore formed therein for receiving a fastening element. The opposedthru-bore tabs in the superior portion are preferably angled toward oneanother in a posterior direction, and the thru-bore tabs in the inferiorportion are also preferably angled toward one another in a posteriordirection. The superior and inferior portions of the plate can also beangled in a direction anterior to an anterior face of a mid-portion ofthe plate, such that the mid-portion of the plate is flush or sub-flushrelative to an anterior face of the adjacent vertebrae.

In yet another embodiment of the present invention, a spinal fixationassembly is provided including a fusion cage with posterior, anterior,superior, and inferior faces, and a plate having at least one aperturefor receiving a bone screw and being configuration to slidably mate tothe fusion cage. In one embodiment, the plate includes a mating elementfor engaging the cage in an anterior-posterior direction. The matingelement can have a variety of configurations, but it preferably takesthe form of opposed first and second arms that are adapted to engage thesuperior and inferior faces of the fusion cage. The first and secondarms can be flexible, and preferably extend from the plate and areadapted to seat on the superior and inferior faces of the fusion cage.The superior and inferior faces of the fusion cage can each include anarm-seating recess formed therein for receiving the first and secondarms on the plate. These recesses allow the arms to sit flush with thesuperior and inferior faces when disposed within the arm-seatingrecesses. In an exemplary embodiment, the first and second arms areadapted to mate with the arm-receiving recesses formed on the fusioncage with an interference fit to temporarily secure the plate to thefusion cage.

In another embodiment, the anterior face of the fusion cage can includeat least one bore formed therein, and the mating element can be at leastone arm that is adapted to extend into the bore in the fusion cage tomate the plate to the fusion cage. In a preferred embodiment, theanterior face of the fusion cage includes a superior bore and aninferior bore formed therein, and the mating element comprises opposedfirst and second arms that are adapted to extend into the superior andinferior bores in the fusion cage to mate the plate to the fusion cage.

In another embodiment, the fusion cage includes an intermediate planethat separates the inferior face from the superior face to define aninferior side and a superior side, and the plate includes at least oneinferior aperture on the inferior side of the fusion cage and at leastone superior aperture on the superior side of the fusion cage. Eachaperture in the plate can have a first end having an opening, a second,opposed end, and a sidewall extending therebetween that defines an innerlumen. The first end of each aperture preferably is a generallyspherical recess formed in the plate for rotatably seating a head of abone screw. A split bushing is preferably disposed within each aperturein the plate. Each aperture can optionally include an anti-rotationmechanism effective to prevent each split bushing from rotating withinthe aperture. The apertures and the split bushings can have a variety ofconfigurations. In one embodiment, the sidewall of each aperture can beconcave and each split bushing can include a convex outer surface. Eachsplit bushing can also optionally include a shoulder formed therein thatabuts a corresponding shoulder formed within each aperture. In anotherembodiment, each split bushing can include an inner surface havingthreads formed thereon that are adapted to mate with correspondingthreads formed on a bone screw.

In other aspects, the inferior and superior apertures are disposed ininferior and superior portions. The portions, or tabs, are preferablyangled with respect to the fusion cage in a direction anterior to theanterior face of the fusion cage. In an exemplary embodiment, eachportion extends in a plane, and each aperture defines a central axisthat extends through the aperture at an angle with respect to the planeof the portion in which the aperture is disposed.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be more fully understood from the following detaileddescription taken in conjunction with the accompanying drawings, inwhich:

FIG. 1A illustrates an anterior view of one embodiment of a spinalfixation plate in accordance with the present invention;

FIG. 1B is an anterior perspective view of the fixation plate shown inFIG. 1A;

FIG. 1C is a posterior perspective view of the fixation plate shown inFIG. 1A;

FIG. 2A is a cross-sectional view of the fixation plate shown in FIG. 1Ataken along line A-A;

FIG. 2B is a cross-sectional view of the fixation plate shown in FIG. 1Ataken along line B-B;

FIG. 2C is a side view of a portion of a human spine having the fixationplate shown in FIG. 1A implanted therein;

FIG. 3A is side view of an embodiment of a spinal fixation plate that isadapted to mate to a fusion cage;

FIG. 3B is a posterior perspective view of the plate shown in FIG. 3A;

FIG. 4A is a side view of the plate shown in FIGS. 3A and 3B mated toone embodiment of a fusion cage to form a spinal fixation assembly;

FIG. 4B is a perspective view of the fusion cage shown in FIG. 4A;

FIG. 5 is a side view of another embodiment of a spinal fixationassembly;

FIG. 6 is a cut-away view of an aperture, split bushing, and bone screwaccording to another embodiment of the present invention;

FIG. 7 is a side view of one embodiment of a bone screw according to thepresent invention;

FIG. 8 is a cut-away view of another embodiment of an aperture, splitbushing, and bone screw according to the present invention;

FIG. 9 is a side view of another embodiment of a bone screw according tothe present invention; and

FIG. 10 is a cut-away, side view of a plate having apertures adapted toreceive the bone screw shown in FIG. 9.

DETAILED DESCRIPTION OF THE DRAWINGS

In general, the present invention provides a spinal fixation platehaving at least one aperture for receiving a bone screw. The plate isadapted to be attached to adjacent vertebrae to maintain the vertebraein and fixed position and thereby provide biomechanical stability to thevertebra. The plate can be used in connection with a variety of spinalimplants, including inner body fusion devices, fusion cages, bonegrafts, artificial discs, or other vertebral implants, and it canoptionally be adapted for use in both mating or non-mating relationshipswith the inner body fusion devices or other vertebral implant.

FIGS. 1A-2B illustrate one embodiment of spinal fixation plate 10. Ingeneral, the plate 10 has a substantially elongate shape and it includesa mid-portion 12 that is positioned between superior and inferiorportions 14, 16. Each portion 12, 14, 16 includes an anterior face 12 a,14 a, 16 a and a posterior face 12 b, 14 b, 16 b, respectively, and theportions 12, 14, 16 together define a longitudinal axis L extendingtherealong. The mid-portion 12 of the plate 10 also includes opposedlateral sides 12 c, 12 d extending therealong between the superior andinferior portions 14, 16.

As indicated above, the superior and inferior portions 14, 16 areadapted to mate to superior and inferior vertebrae, respectively, andthe mid-portion 12 extends therebetween to maintain the vertebrae at afixed position with respect to one another. Accordingly, the plate 10preferably includes one or more apertures or thru-bores formed thereinfor receiving a fastening element, such as a bone screw, to attach theplate 10 to the adjacent vertebrae. In the illustrated exemplaryembodiment, each portion 14, 16 includes two thru-bores 20 a, 20 b, 22a, 22 b formed therein. The thru-bores 20 a, 20 b, 22 a, 22 b arepreferably formed on opposed sides of the longitudinal axis L of theplate 10 such that each of the superior and inferior portions 14, 16 ofthe plate 10 include first and second opposed thru-bore tabs 15 a, 15 b,17 a, 17 b. The thru-bores 20 a, 20 b, 22 a, 22 b can have a variety ofconfigurations, and exemplary configurations will be discussed in moredetail with respect to FIGS. 6-10.

The superior and inferior portions 14, 16 of the plate 10 can also beadapted to position the thru-bores 20 a, 20 b, 22 a, 22 b at aparticular location with respect to the adjacent vertebrae. In anexemplary embodiment, the superior and inferior portions 14, 16 can beangled with respect to the mid-portion 12 and more particularly, as bestshown in FIG. 2A, the superior and inferior portions 14, 16 can extendin a direction that is anterior to the anterior face 12 a of themid-portion 12. As a result, when the plate 10 is implanted, thesuperior and inferior portions 14, 16 can be positioned on the anteriorrim of each vertebra, which is a location that is between the anteriorface and the endplate of each vertebra, e.g., along an edge of thevertebrae at the endplate/cortical junction. This location, which willbe discussed in more detail with respect to FIG. 2C, is hereinafterreferred to as the anterior rim of a vertebra. When the superior andinferior portions 14, 16 are positioned against the anterior rims, theangle α also causes the mid-portion 12 to be substantially flush orsub-flush with respect to the anterior surface of each vertebra, therebyminimizing the anterior prominence of the plate 10. The position alsoallows locking mechanisms, such as bone screws, to be inserted throughthe thru-bores 20 a, 20 b, 22 a, 22 b, through the anterior rims of thevertebrae, and into the vertebral bodies. The unique positioning of theplate 10 also reduces the need for excessive vessel retraction.

The angulation of the superior and inferior portions 14, 16 can varydepending on the intended use, but in an exemplary embodiment the angleα_(T) between the anterior surface 14 a, 16 a of the superior andinferior portions 14, 16 and the anterior surface 12 a of themid-portion 12 is less than about 15°, and more preferably the angleα_(T) is about 10°. A person having ordinary skill in the art willappreciate that the angle α_(T) can be greater than 15°.

The plate 10 can also or alternatively have a curve X, as best shown inFIGS. 1B, 1C, and 2B, that is formed about the longitudinal axis L in asagittal plane, which extends in a superior-inferior direction anddissects the posterior and anterior faces 12 a, 12 b, 14 a, 14 b, 16 a,16 c of the plate 10. The curve X is preferably only formed about thelongitudinal axis L that extends between the superior and inferiorportions 14, 16. More particularly, the plate 10 can be curved such thatthe opposed edges 12 c, 12 d of the mid-portion 12 are substantiallylongitudinally straight, but they are positioned posterior to theposterior face 12 b of the mid-portion 12. As a result of the curve X,the posterior face 12 b, 14 b, 16 b of each portion 12, 14, 16 can havea substantially concave shape about the longitudinal axis L. Theanterior face 12 a, 14 a, 16 a of each portion 12, 14, 16 can alsooptionally have a substantially convex shape about the longitudinal axisL to correspond to the posterior face 12 b, 14 b, 16 b.

The curve X can also continue through the superior and inferior portions14, 16 of the plate 10, such that the opposed edges 14 c, 14 d, 16 c, 16d of the superior and inferiors portions 14, 16 are positioned posteriorto the posterior faces 14 b, 16 b thereof. As previously discussed, thesuperior and inferior portions 14, 16 can also be angled in a directionanterior to the anterior faces 14 a, 16 a thereof. When the angle α_(T)and the curve X are combined, the opposed thru-bore tabs 15 a, 15 b, 17a, 17 b are not only angled anterior to the anterior face 12 a of themid-portion 12 of the plate 10, but they are also angled toward oneanother in a posterior direction. While the angle α_(x), shown in FIGS.1C and 2B, can vary, in an exemplary embodiment the angle α_(x) betweenthe thru-bore tabs 15 a, 15 b, 17 a, 17 b is in the range of about 150°to 180°, and more preferably the angle is about 160°. A person skilledin the art will appreciate that where the angle α_(x) is 180°, the plate10 will not have a curve X formed therein, but rather it will besubstantially planar.

In use, the plate 10 can be implanted in the lumbar, cervical, orthoracic regions of the patient's spine, and thus the size of the plate10 will vary depending on the intended use. The plate 10 can also beadapted for use in various surgical approaches, but preferably the plate10 is adapted for anterior fixation. In an exemplary embodiment, theplate 10 has a length l and/or width w that is adapted for use in thelumbar region of a patient's spine. More preferably, the plate 10 has alength l that is less than a distance between the adjacent vertebrae towhich the plate 10 is adapted to be mated to. This allows the superiorand inferior portions 14, 16 of the plate 10, and in particular thethru-bore tabs 15 a, 15 b, 17 a, 17 b, to be positioned on the anteriorrims of the adjacent vertebrae, as previously discussed above. A personskilled in the art will appreciate that the plate 10 can be adapted fora variety of other uses and the configuration of the plate 10 can varydepending on the intended use. Moreover, a variety of plates 10 havingvarious sizes and configurations can be provided as part of a kit,allowing a surgeon to select the appropriate plate 10 based on theintended use.

By way of non-limiting example, FIG. 2C illustrates plate 10 implantedin a patient's spinal column. In particular, the plate 10 is shown matedto adjacent vertebrae 50, 52 having an implant, e.g., fusion cage 30,disposed therebetween. The adjacent vertebrae 52, 54 are distracted, atleast a portion of the disc is removed, and the area is prepared usingtechniques known in the art. Prior to inserting the fusion cage 30between the adjacent vertebrae 52, 54, the fusion cage 30 can be filledwith autograft, allograft bone, and/or demineralized bone matrix topromote fusion. The fusion cage 30 is then positioned between thevertebrae 52, 54 using a variety of devices. Distractor and spreaderdevices are known in the art, and are effective for separating adjacentvertebrae, and optionally assisting with insertion of the implant.Typical distractors include two opposed blade members which are insertedbetween the adjacent vertebrae, and then opened to separate thevertebrae. The fusion cage 30 can then be inserted into the disc spaceeither manually, or using an impacting device, such as a mallet.

Once the fusion cage is in position, the fixation plate 10, and inparticular the posterior surface 12 b of the plate 10, can be placedadjacent to the anterior face 32 of the fusion cage 30 to position thesuperior and inferior portions 14, 16 of the plate 10 against theanterior rims 52 a, 54 a of the adjacent vertebrae 52, 54. Oncepositioned against the vertebrae, the plate 10 is preferably not fixedlyattached to the fusion cage 30 such that the two components are in anon-mating relationship with one another. In other words, the plate 10and the fusion cage 30 remain as separate components from one another.One or more bone screws (only two screws 62 a, 64 are shown) can then beinserted through the thru-bores 20 a, 20 b, 22 a, 22 b in the superiorand inferior portions 14, 16 of the plate 10 to secure the plate 10 tothe adjacent vertebrae 52, 54. A person skilled in the art willappreciate that various procedures and tools can be used to position theplate 10 against the adjacent vertebrae and to prepare the vertebrae forreceiving the bone screws. The plate 10 can also optionally includevarious features to allow the plate 10 to be coupled to a tool forimplanting the plate 10.

FIGS. 3A-3B illustrate another embodiment of a spinal fixation plate120. In this embodiment, the plate 120 is adapted to mate to a vertebralimplant, such as a fusion cage 110, shown in FIGS. 4A-4B. FIG. 4Aillustrates plate/cage assembly 100. The plate 120 can have a generallyplanar shape and it includes a mid-portion 126 that is positionedbetween superior and inferior portions 128, 130. When the plate 120 ismated to the fusion cage 110, the superior portion 128 of the plate 120is adapted to extend beyond a superior surface 102 of the fusion cage110, and the inferior portion 130 of the plate 120 is adapted to extendbeyond an inferior surface 104 of the fusion cage 110. While the plate120 is preferably substantially planar, the mid-portion 126 of the plate120 can be curved to contour the shape of an anterior face 108 of thefusion cage 110.

Each of the superior and inferior portions 128, 130 of the plate 120further include at least one aperture 122 a-d formed therein forreceiving a bone screw to secure the plate 120 to a vertebra. As shown,the superior and inferior portions 128, 130 of the plate 120 eachinclude two apertures 122 a, 122 b, 122 c, 122 d formed therein. Theapertures 122 a-d can have a variety of configurations, and exemplaryconfigurations will be discussed in more detail with respect to FIGS.6-10. FIGS. 4A-4B illustrate plate 120 mated to implant 110, andapertures 122 a-d having bone screws 146 and 148 disposed therethrough,each having a head and a shank.

The superior and inferior portions 128, 130 of the plate 120 can alsoextend at an angle with respect to the mid-portion 126 of the plate 120.In particular, referring to FIG. 4A, which shows plate 120 mated to cage110, superior and inferior portions 128, 130 are angled with respect tothe remainder of the plate 120 so that screws 146 and 148 extendingtherethrough are angled with respect to a medial plane “P” of the body110. The angle formed by the tab(s) and plate, as well as by thescrew(s) and medial plane, is designated as “α” and it can varydepending on a patient's particular anatomy. Although the angle α canrange from 15° to 60°, for most applications the angle α is about 20°.However, in other embodiments, the superior and inferior portions 128,130 can be flexible or readily bent with respect to the remainder of theplate 120.

The mid-portion 126 of the plate 120 can also include a central aperture132 formed therein. The central aperture 132 is positioned such that itis aligned with a central bore (not shown) formed in the fusion cage 110when the plate 120 is mated to the cage 110. The central aperture 132and bore can be effective to receive an insertion tool and/or afastening element, such as a screw, effective to mate the plate 120 tothe fusion cage 110. In one embodiment (not shown), the fasteningelement can be fixedly, but rotatably disposed within the centralaperture 132 of the plate 120, and/or it can be adapted to snap into thecentral bore in the fusion cage 110. The fastening element can furtherbe adapted to engage the fusion cage 110 upon rotation thereof. A personhaving ordinary skill in the art will appreciate that a variety oftechniques can be used to mate the plate 120 to the fusion cage 110.

Still referring to FIGS. 3A-4B, the plate 120 can also include a matingelement 124 a, 124 b that is adapted to slidably engage and mate theplate 120 to the anterior face 108 of the fusion cage 110 in ananterior-posterior direction. While the mating element 124 a, 124 b canhave a variety of configurations, FIGS. 3A-3B illustrate first andsecond opposed arms 124 a, 124 b that extend outward from the plate 120in a direction substantially perpendicular to the substantially planarsurface of the plate 120. The arms 124 a, 124 b can be positionedanywhere on the plate 120, but preferably the first arm 124 a ispositioned just superior to the mid-portion 126 of the plate 120 betweenthe central aperture 132 and the superior apertures 122 a, 122 b formedin the superior portion 128 of the plate 120, and the second arm 124 bis positioned just distal to the mid-portion 126 of the plate 120between the central aperture 132 and the inferior apertures 122 c, 122 dformed in the inferior portion 130 of the plate 120. In other words, thearms 124 a, 124 b are positioned such that, when the plate 120 is matedto the fusion cage 110, the arms 124 a, 124 b are configured to engagethe superior and inferior faces 102, 104 of the fusion cage 110.

The shape of the arms 124 a, 124 b can also vary, but preferably eacharm 124 a, 124 b is adapted to contour the shape of the fusion cage 110.By way of non-limiting example, where the fusion cage 110 has domed orconvex superior and inferior surfaces 102, 104, the arms 124 a, 124 bare preferably convex to contour the shape of the fusion cage 110. Thesize of each arm 124 a, 124 b can vary as well, but preferably each arm124 a, 124 b has a length l_(a) sufficient to enable the arms 124 a, 124b to extend across at least a portion of the superior and inferiorsurfaces 102, 104 of the fusion cage 110, and a width w_(a) sufficientto allow the arms 124 a, 124 b to grasp the fusion cage 110.

Each arm 124 a, 124 b can have a variety of configurations, butpreferably the arms 124 a, 124 b include an engagement element 136 a,136 b effective to engage the superior and inferior faces 102, 104 ofthe fusion cage 110. The engagement element 136 a, 136 b preferablyprovides an interference fit to temporarily secure the plate 120 to thefusion cage 110. While the engagement element 136 a, 136 b can have avariety of configurations, the engagement element 136 a, 136 b can be,for example, in the form of at least one protrusion formed on an innersurface of each arm 124 a, 124 b that is adapted to sit in at least oneindentation 138 (shown in FIG. 4B) formed in each of the superior andinferior faces 102, 104 of the fusion cage 110. As shown in FIG. 3A, theprotrusion 136 a, 136 b on each arm 124 a, 124 b has a generallyelongate shape. The indentation will be discussed in more detail withrespect to FIG. 4B below. The arms 124 a, 124 b can optionally beflexible to allow the arms 124 a, 124 b to flex outward while slidingthe plate 120 onto the fusion cage 110, and to allow the arms 124 a, 124b to then return to their original state whereby the protrusions 136 a,136 b on the arms 124 a, 124 b to snap into the indentations 138 (onlyone indentation is shown in FIG. 4B) formed in the superior and inferiorfaces 102, 104 of the fusion cage 110.

Referring now to FIG. 4B, fusion cage 110 is shown in more detail. Thefusion cage 110 can have a variety of configurations, but as previouslystated it generally includes superior 102, inferior 104, posterior 106,and anterior 108 faces. The inferior and superior faces 102, 104 canhave a flat to slightly convex shape, and/or a slightly tapered (about10°) or wedge profile, wherein the body 110 is thicker at the anteriorface 108 than at the posterior face 106.

A central bore (not shown) can be formed in the anterior face 102 of thefusion cage 110, and it preferably includes threads formed therein forreceiving a fastening element, e.g., a screw. The threads are preferablyspinal lock threads to provide a secure connection between the plate andthe cage. First and second transverse elements 140, 142 can join theposterior face 106 to the anterior face 108, and a guide path 144 forreceiving an insertion tool can extend across the superior and inferiorfaces 102, 104 between the posterior and anterior faces 106, 108.

Fusion cage 110 further includes an arm-seating recess formed in each ofthe superior and inferior surfaces 102, 104 for receiving the arms 124a, 124 b formed on the plate 120. The recesses can be formed in theguide path 144, or more preferably the guide path 144 can formarm-seating recesses, as is shown in FIG. 4B. Each guide path 144 (onlythe guide path on the superior surface 102 is shown), or arm-seatingrecess, preferably has a depth d sufficient to receive the correspondingarm 124 a, 124 b formed on the plate 120 such that, when the plate 120is mated to the fusion cage 110, the arms 124 a, 124 b are flush withthe superior and inferior surfaces 102, 104 of the fusion cage 110. Thisis particularly advantageous in that it allows the fusion cage 110 to bepositioned between adjacent vertebrae prior to inserting the arms 124 a,124 b into the arm-seating recesses 144 to attach the plate 120 to thefusion cage 110. Each of the arm-seating recesses 144 further preferablyincludes at least one indentation 138 formed therein for receiving theprotrusion 136 a, 136 b formed on the inner surface of each arm 124 a,124 b. As shown, the indentation 138 is in the form of an elongategroove that is adapted to receive and seat the protrusion 136 a, 136 bformed on each arm 124 a, 124 b. A person having ordinary skill in theart will appreciate that the arms 124 a, 124 b can merely slid into andseat within the recess 144 formed in the fusion cage 110, and that theydo not need to engage the fusion cage 110. An engagement mechanism ismerely preferred to allow the plate 120 to be at least temporarilysecured to the fusion cage 110 during implantation.

The fusion cage 110 can optionally include a number of bone engagingsurface features 146 formed on the superior and inferior surfaces 102,104 to facilitate the secure mounting of the cage 110 between adjacentvertebrae. The bone engaging surface features 146 can be present on theentire surface area of the superior and inferior surfaces 102, 104, oroptionally, selected regions of the superior and inferior surfaces 102,104 can be free of surfaces features 146. The bone engaging surfacefeatures 146 can have a variety of shapes, but are preferably in theform of wedge-shaped ridges that extend is a direction transverse to theposterior 106 and anterior 108 faces of the fusion cage 110. Each boneengaging surface feature 146 includes a posterior side wall 148 and ananterior side wall 149, which meet at a peak 150. The side walls 148,149 of each surface feature 146 can be angled or sloped to facilitateinsertion of the cage 110 between adjacent vertebrae and to assist inpreventing the fusion cage 110 from becoming dislodged. The size of thesurface features 146 can also vary but preferably the surface features146 have a size sufficient to cause each surface feature 146 to engageand penetrate the adjacent vertebrae. It will be understood that whileridges 146 have been shown in a preferred embodiment, it is contemplatedthat there are a variety of structures which could provide a surface foreffective engagement with the vertebral bodies to limit expulsion fromthe disc space.

FIG. 5 illustrates another embodiment of a spinal fixation assembly100′. In this embodiment, the arms 124 a, 124 b on the plate 120 areadapted to extend into opposed superior and inferior bores 152, 154,rather than recesses 144, formed in the fusion cage 110′. As shown, thearms 124 a, 124 b can merely slide into the bores 152, 154 that extendinto the fusion cage 110′ to provide an alignment mechanism between thecage 110′ and the plate 120. The bores 152, 154 can optionally beadapted to receive the engagement mechanism 136 a, 136 b formed on eacharm 124 a, 124 b to at least temporarily secure the arms 124 a, 124 bwithin the bores 152, 154. By way of non-limiting example, the arms 124a, 124 b and the bores 152, 154 can each be tapered to provide aninterference fit between the arms 124 a, 124 b and the bores 152, 154.Alternatively, the arms 124 a, 124 b can include a press-fit pin thatdepresses upon insertion of the arms 124 a, 124 b into the bores 152,154, and then once each arm 124 a, 124 b is fully inserted into the bore152, 154, returns to its originally state whereby the pins extendinginto corresponding indentations formed within the bores 152, 154. Aperson having ordinary skill in the art will appreciate that a varietyof mechanisms can be used to secure the arms 124 a, 124 b of the plate120 within the bores 152, 154 formed in the fusion cage 110′.

In use, the adjacent vertebrae are prepared and distracted and thefusion cage 110 is placed therebetween, as previously described above.Once the fusion cage 110 is in position, the fixation plate 120 can beplaced adjacent to the anterior face 108 of the fusion cage 110 toposition the superior and inferior portions 128, 130 of the plate 110against the anterior rims of the adjacent vertebrae. The plate 120 isthen preferably mated to the anterior face 108 of the fusion cage 110 bypositioning the arms 124 a, 124 b between the superior and inferiorsurfaces 102, 104 of the fusion cage 110 and the adjacent vertebrae.Where plate 120′ is used and the cage 110′ includes arm-receivingrecesses 152, 154, the arms 124 a′, 124 b′ of the plate 120′ can beeasily slid into the recesses 152, 154 to engage the cage 110′. A centerscrew (not shown) can then be inserted through a central aperture 132 inthe plate 120 and through a bore in the cage (e.g., FIG. 5 shows bore134 formed in the cage 110′) to secure the plate 120 to the cage 110,and one or more bone screws (only two bone screws 146, 148 are shown inFIG. 4A) can be inserted through the apertures 122 a, 122 b, 122 c, 122d in the superior and inferior portions 128, 130 of the plate 120 tosecure the plate 120 to the adjacent vertebrae.

The present invention also provides a variety of configurations forsecuring a spinal fixation plate to adjacent vertebrae. In particular,FIGS. 6-10 illustrate embodiments of different apertures for use with aplate according to the present invention. The apertures are adapted toprovide a more secure connection between the plate and a vertebrae.While the various embodiments will be described in relation toparticular spinal fixation plates disclosed herein, a person havingordinary skill in the art will appreciate that the virtually anytechnique known in the art can be used with any of the variousembodiments of spinal fixation plates, as well as with a variety ofvertebral implants.

FIG. 6 illustrates one embodiment of an aperture 160 formed in a tab 166of a plate and having a split bushing 162 disposed therein. A bone screw174 is disposed through the aperture 160 and the split bushing 162. Theaperture 160 includes a first end 168, a second end 170, and a sidewall172 extending therebetween. The first end 168 is preferably adapted toreceive a bone screw 174, or similar type of fixation element, and toseat the head 164 of the bone screw 174 therein. The aperture 160 canextend through the tab 166 in the plate along a central axis a_(a) thatis substantially perpendicular to a central plane a_(p) of the tab 166,or alternatively the central axis a_(a) of the aperture 160 can beoffset from, or disposed at an angle with respect to, the plane a_(p) ofthe tab 166. The sidewall 172 of the aperture 160 can also vary and canbe either substantially planar along the length thereof between thefirst and second ends 168, 170 of the aperture 160, or the sidewall 172can be curved or can extend at an angle. As shown in FIG. 6, thesidewall 172 has a substantially concave shape to receive the splitbushing 162.

The split bushing 162 is disposed within the aperture 160 and it has agenerally cylindrical shape with a gap (not shown) formed therein toallow the bushing 162 to be expanded. The split bushing 162 includes anouter surface 176 which can have a shape adapted to conform to the shapeof the sidewall 172 of the aperture 160, and an inner surface 178 whichis adapted to receive a bone screw 174. By way of non-limiting example,the split bushing 160 can have a convex outer surface 172 to allow thesplit bushing 162 to sit within the concave sidewall 172 of the aperture160. The split bushing 162 further includes an inner diameter d_(b) thatcan vary between opposed first and second ends 168, 170 of the splitbushing 162. Preferably, the diameter d_(b) of the bushing 162 at thefirst end 168 is larger than the diameter d_(b) of the bushing 162 atthe second end 170. The tapered diameter allows the bushing 162 toreceive a portion of the tapered undersurface of the head 164 of thebone screw 174.

FIG. 7 illustrates the bone screw 174 in more detail having a taperedhead 164 adapted to fit within the split bushing 162 shown in FIG. 6. Asshown, the bone screw 174 includes a head 164 and a threaded shank 180.The head 164 is tapered preferably at an angle substantially the same asthe angle of the tapered inner diameter d_(b) of the split bushing 162.In use, upon tightening the bone screw 174, the split bushing 162expands and provides an interference fit between the bone screw 174 andthe aperture 160, thereby creating a rigid lock to secure the plate to avertebrae. The tapered diameter d_(b) of the bushing 162 also allows thebone screw 174 to be inserted at variable angles a_(s) with respect tothe central axis a_(a) of the aperture, as shown in FIG. 6.

FIG. 8 illustrates another embodiment of an aperture 190 having a splitbushing 192 disposed therein. In this embodiment, the split bushing 192includes threads 194 formed on an inner surface thereof to mate withcorresponding threads 196 formed on a bone screw 198. The threads 194,196 are particularly effective to prevent the bone screw 198 frombacking out of the aperture 190, and to provide a rigid lock between thescrew 198 and the aperture 190 thereby securely mating the plate to avertebrae. In this embodiment, the aperture 190 preferably includes ananti-rotation mechanism effective to prevent the split bushing 192 fromrotating while the screw 198 is threaded therethrough. The anti-rotationmechanism can have a variety of configurations and, by way ofnon-limiting example, can be a pin or raised protrusion (not shown)disposed within the aperture 190 and adapted to extend into the gapformed in the split bushing 192.

FIGS. 9-10 illustrate yet another embodiment of an aperture 200 and bonescrew 202 for use with the present invention. As shown in FIG. 10, theaperture 200 includes a first end 204, a second end 206, and a sidewall208 extending therebetween and defining an inner lumen 210. The innerlumen 210 includes a first portion 214 positioned adjacent the first end204, and a second portion 212 positioned adjacent the second end 206 ofthe aperture 200. The first portion 214 of the inner lumen 210 has ashape and size adapted to receive the head 216 of a bone screw 202. FIG.9 illustrates an exemplary embodiment of a bone screw 202 for use with aplate having an aperture 200 as shown in FIG. 10. The bone screw 202includes a head 216 and a threaded shank 218. The head 216 of the bonescrew 202 includes a substantially convex, slightly rounded outersurface 220. The first portion 214 of the inner lumen 210 of theaperture 200 has a concave sidewall 222, e.g., a generally sphericalrecess, to allow the rounded head 216 of the bone screw 202 to seattherein. The second portion 212 of the inner lumen 210 is substantiallycylindrical and has a shape and size adapted to receive the threadedshank 218 of a bone screw 202. Preferably, the second portion 212 of theinner lumen 210 has a diameter d₂ greater than a diameter d₁ of theshank 218 of the bone screw 202. In use, the first and second portions214, 212 of the inner lumen 210 allow the bone screw 202 to translatewithin the aperture 200 such that the screw 202 can be inserted atvarying angles. While the aperture 200 does not include a split bushingto provide a rigid connection between the bone screw 202 and the plate,the aperture 200 allows the full exertion of natural biomechanicalcompression stresses through the vertebral bodies into which the screw202 is inserted.

Referring back to FIG. 7, in yet another embodiment, the bone screw 174can include a shoulder 230 formed thereon that abuts a correspondingshoulder (not shown) formed in an aperture. The shoulder 230 is formedby a difference, or stepped increase, in the diameter d₃, d₄ of thescrew head 164 and in the diameter of the aperture, or in the splitbushing if the aperture includes one. In use, the bone screw 174 isinserted through an aperture and once the shoulder 230 on the screw head164 passes the shoulder 230 in the aperture, or in the split bushing,the shoulders will engage thereby preventing the screw 174 from backingout of the aperture.

The fusion cage and plate of the present invention can be made from avariety of materials. By way of non-limiting example, a carbon fibercomposite or other radiolucent material is well suited for fabricationof the body, and titanium or carbon fiber composites are suitablematerials for the plate 20.

As should be readily apparent from the preceding description, thepresent invention provides many advantages. For example, the fusion cagecan be sufficiently broad and thick so that only a single cage is neededto replace an excised disc. The profile and slightly bowed or convexsuperior and inferior surfaces of the fusion cage body closelyapproximate the shape of a natural disc and provide an excellent,stable, load-bearing surface. The plate, when included, ensures that thebody will not become dislodged from the spine, yet is readily accessiblewith an anterior approach. Further, the plate allows bone screws to bedeeply embedded into the vertebral bodies without piercing or otherwisedamaging the hard, load-bearing, cortical bone. Also, both the plate andthe body include features that allow for relatively easy manipulationand insertion with appropriately configured surgical tools.

Of course, one skilled in the art will appreciate further features andadvantages of the invention based on the above-described embodiments.Accordingly, the invention is not to be limited by what has beenparticularly shown and described, except as indicated by the appendedclaims. All publications and references cited herein are expresslyincorporated herein by reference in their entirety.

What is claimed is:
 1. A spinal fixation assembly, comprising: a fusioncage having an anterior face and a posterior face, and a superior faceand an inferior face, the fusion cage being configured to be positionedbetween adjacent vertebrae such that at least a portion of the superiorface contacts an endplate of a superior vertebra and at least a portionof the inferior face contacts an endplate of an inferior vertebra, thefusion cage having a first recess disposed in the superior face and asecond recess disposed in the inferior face; and a spinal fixation platehaving an anterior face and a posterior face, at least one bone screwaperture extending through the anterior and posterior faces forreceiving a bone screw configured to mate the spinal fixation plate tobone, the at least one bone screw aperture being obliquely angledrelative to the posterior and anterior faces of the spinal fixationplate, a central opening being disposed substantially at a center of thespinal fixation plate, and first and second arms extending outward fromthe posterior face of the plate, the first and second arms beingconfigured to slidably contact the fusion cage such that the first armextends across and contacts the first recess of the fusion cage and thesecond arm extends across and contacts the second recess of the fusioncage.
 2. The spinal fixation assembly of claim 1, wherein the at leastone bone screw aperture comprises first and second bone screw aperturespositioned on opposite sides of the central opening.
 3. The spinalfixation assembly of claim 1, wherein the first and second arms eachhave a central longitudinal axis that is non-parallel to a centrallongitudinal axis of the at least one bone screw aperture.
 4. The spinalfixation assembly of claim 1, wherein the superior and inferior faces ofthe fusion cage include bone engaging surface features formed thereon.5. The spinal fixation assembly of claim 1, wherein the at least onebone screw aperture has an inner sidewall that is substantially concavefor polyaxially seating a bone screw.
 6. The spinal fixation assembly ofclaim 1, further comprising at least one locking feature configured toprevent the spinal fixation plate from moving relative to the fusioncage in the direction substantially perpendicular to the posterior faceof the fusion cage.
 7. The spinal fixation assembly of claim 1, whereinwhen the first and second arms are received in the first and secondrecesses, the first and second arms engage the fusion cage.
 8. A spinalfixation assembly, comprising: a fusion cage having superior andinferior bone-contacting surfaces, and at least one arm-guide formedtherein; a spinal fixation plate having first and second bone screwbores formed therein, and at least one arm formed thereon and configuredto extend into the at least one arm-guide in the fusion cage, the firstand second screw bores each having a central longitudinal axis thatextends at an acute angle relative to first and second faces of thespinal fixation plate; and first and second bone screws configured toextend respectively through the first and second bone screw bores formating the spinal fixation plate to bone; wherein the spinal fixationplate includes an opening formed therein and positioned along ahorizontal longitudinal axis of the plate and a screw received in theopening; wherein the first and second bone screw bores are offset fromthe horizontal longitudinal axis, the first bone screw bore beingpositioned on a first side of the horizontal longitudinal axis and thesecond bone screw bore being positioned on a second side of thehorizontal longitudinal axis; wherein, when the first and second bonescrews are disposed through the first and second bone screw bores, adistance between each of the first and second bone screws and one of thesuperior and inferior surfaces of the fusion cage increases in adirection from the second face of the spinal fixation plate to distalends of the first and second bone screws.
 9. The spinal fixationassembly of claim 8, wherein the at least one arm has a centrallongitudinal axis that is non-parallel to a central longitudinal axis ofeach of the first and second bone screw bores.
 10. The spinal fixationassembly of claim 8, wherein when the at least one arm of the spinalfixation plate is coupled to the at least one arm guide, the at leastone arm is flush with an outer surface of the fusion cage.
 11. Thespinal fixation assembly of claim 8, wherein the superior and inferiorsurfaces of the fusion cage include bone engaging surface featuresformed thereon.
 12. The spinal fixation assembly of claim 8, wherein thefirst and second bone screw bores each have an inner sidewall that issubstantially concave, and wherein the first and second bone screws eachhave a head with a substantially convex outer surface for seating withinthe first and second bone screw bores.
 13. The spinal fixation assemblyof claim 8, further comprising a central bore formed in the fusion cage,wherein the opening formed in the spinal fixation plate is configured tobe coaxially aligned with the central bore.
 14. The spinal fixationassembly of claim 8, further comprising at least one pin configured tolock the spinal fixation plate relative to the fusion cage, therebypreventing the spinal fixation plate from moving relative to the fusioncage in the direction substantially perpendicular to a first face of thefusion cage.
 15. A spinal fixation assembly, comprising: a fusion cagehaving an anterior face and a posterior face, and a superior face and aninferior face, the superior face comprising a superior-facingbone-engaging surface and a superior-facing recessed surface that isopen to a superior end of the cage and the inferior face comprising aninferior-facing bone-engaging surface and an inferior-facing recessedsurface that is open to an inferior end of the cage, the fusion cagebeing configured to be positioned between adjacent vertebrae such thatthe superior-facing bone-engaging surface contacts an endplate of asuperior vertebra and the inferior-facing bone-engaging surface contactsan endplate of an inferior vertebra; and a spinal fixation plate havingan anterior face and a posterior face, at least one bone screw apertureextending through the anterior and posterior faces for receiving a bonescrew configured to mate the spinal fixation plate to bone, the at leastone bone screw aperture being obliquely angled relative to the posteriorand anterior faces of the spinal fixation plate, a central opening beingdisposed substantially at a center of the spinal fixation plate, andfirst and second arms extending outward from the posterior face of theplate, the first and second arms being configured to slidably contactthe fusion cage such that the first arm extends along thesuperior-facing recessed surface of the fusion cage and the second armextends along the inferior-facing recessed surface of the fusion cage.16. The spinal fixation assembly of claim 15, wherein when the arms ofthe spinal fixation plate contact the fusion cage, a superior surface ofthe first arm is flush with the superior bone-engaging surface of thefusion cage and an inferior surface of the second arm is flush with theinferior bone-engaging surface of the fusion cage.
 17. The spinalfixation assembly of claim 15, wherein the at least one bone screwaperture comprises first and second bone screw apertures positioned onopposite sides of the central opening.
 18. The spinal fixation assemblyof claim 15, wherein the first and second arms each have a centrallongitudinal axis that is non-parallel to a central longitudinal axis ofthe at least one bone screw aperture.
 19. The spinal fixation assemblyof claim 15, further comprising at least one locking feature configuredto prevent the spinal fixation plate from moving relative to the fusioncage in a direction substantially perpendicular to the posterior face ofthe fusion cage.
 20. The spinal fixation assembly of claim 15, whereinwhen the first arm extends along the superior-facing recessed surfaceand the second arm extends along the inferior-facing recessed surface,the first and second arms engage the fusion cage.